The present invention relates generally to a forward observation system and, more particularly, to an enhanced precision forward observation system and method using a satellite positioning system receiver integrated with a laser range finder and compass. The position may be used with target position estimation software for improved target position estimation.
The forward observation problem involves observing potential enemy targets to determine their location. The technology used in performing forward observation varies from quite basic to very sophisticated.
For example, latitude and longitude may be calculated by an observer located near or at the target site. Such observations may be based on a visual estimate of target position relative to a landmark or other feature of known coordinates, e.g., a feature shown on a map, or by using triangulation techniques. The coordinates of a target may also be fairly accurately calculated by such a person in the vicinity of the target using astronomical or celestial positioning techniques, particularly when there are no landmarks of known position available. Similarly, a person in the vicinity of the target with a satellite positioning system receiver, e.g., a Global Positioning System (GPS) receiver, may be employed for an accurate determination of target position.
Because sending and retrieving an observer from the target vicinity puts the observer at risk of being located by the enemy and creates the potential for fratricide, it would be desirable to provide a system and method for accurate forward observation that can be performed at long range.
Although sophisticated forward observation systems may include a laser range finder, a compass and inclinometer (or other attitude measurement system), and a GPS receiver, or perhaps a radar integrated with a gyroscope, there is no system which addresses the three types of errors inherent in a forward observation target solution, namely, measurement errors, systematic errors, and operator errors.
Measurement Errors.
Existing forward observation systems calculate target location using a single measurement set from a laser range finder, compass, and inclinometer, to obtain range and bearing information about potential targets. This information is used to calculate a directed distance which is then coordinated with maps to plot target coordinates. Such methods provide good distance accuracy, i.e., along track accuracy, due to the accuracy of laser ranging. However, the azimuth or angular measurement accuracy, i.e., cross track accuracy, will generally be poor, given compass inaccuracies (e.g., regional or localized variations between true north and magnetic north) and the multiplicative effect of range on the angular error. The resulting error distribution exhibits elliptical bivariate Gaussian distribution characteristics, with the major axis along the cross track direction. The major to minor axis ratios can be extreme for long range forward observation (approximately 50:1 at four kilometers). This results in a circular error probable (CEP) radius that is nearly the size of the major axis radius, resulting in poor target position estimation. Additionally, with traditional methods, the CEP radius is unknown, resulting in an unknown kill ratio until after firing and impact assessment is complete.
In addition to the measurement errors which occur even if both human and equipment portions of the targeting system work properly, there are systematic and operator errors which can overwhelm all other error sources.
Systematic Errors.
The primary systematic error is the magnetic variance of the compass being used to measure azimuth. This effect can cause very large errors in the compass measurement, e.g., errors greater than 10 degrees. Even with magvar corrections, the applied error can still be several degrees.
Operator Errors.
Operator errors consist primarily of the operator accidentally measuring something other than what was intended. Failure to detect this when performing multiple measurements of the same target could yield dramatic and unknown errors.
It is, therefore, apparent that there exists a need for a forward observation system and method that integrates a laser range finder and an attitude measurement device with a satellite positioning system receiver to provide precise target positioning and overcomes measurement, systematic, and operator error.